The Oracle

The Oracle is a monster who resides on a special level called "The Oracle Level" (or Delphi). She can provide a consultation for a fee, which is supposed to be one of the main ways the player learns about the game. In practice, players read spoilers, such as this one.

Level

The Oracle Level is located between level 5 and 9 inclusive in the Dungeons of Doom. It is eligible to leave bones, and monster creation is biased towards neutral monsters. Immediately below the Oracle Level is the level with the entrance to Sokoban.

There are five rooms to the sides of the above area, containing the stairs (in separate rooms), five random monsters, three random traps, and six random items; they are linked to each other and to the above room by corridors. Each room has one trap, except the rooms with two objects or with the stairs up. The Oracle is at the center of the three by three room (called Delphi), amid the fountains. Delphi has a random empty doorway in one wall. There are two random monsters generated in the area surrounding Delphi. The marked statues are:

The Oracle is a human @, and always starts peaceful. Attacking her in melee causes a spray of magic missiles to hit you; she has no active attacks of her own.[1] If you survive these magic missiles and #chat with her, you will get the message "The oracle is in no mood for consultations." Killing her with ranged attacks will net no penalty except that of murder, but it's generally a bad idea.

The passive magic missile attack is not implemented for inter-monster combat in vanilla nethack, so any pet at level 11 or higher will attack and may kill the oracle. SLASH'EM and UnNetHack implement this passive attack; additionally, in SLASH'EM, if a woodchuck is the attacker the message associated with the attack is "ZOT!"[2]

Consultations

The Oracle offers two services. Minor consultations are true rumors, like you get from a blessed fortune cookie. A major consultation is an extended description of some aspect of the game, for example:

Behold the cockatrice, whose diminutive stature belies its hidden might. The
cockatrice can petrify any ordinary being it contacts--save those wise
adventurers who eat a dead lizard or blob of acid when they feel themselves
slowly turning to stone.

Major consultations can be found in the file oracles.txt, for players who are not inclined to pay as they go.

Consultations cost money, but the first major and the first minor consultation you buy each increases your score[3] and gives experience points[4]. Buying a consultation of a type you've already bought gives neither experience nor score.

If you take a major consultation, but do not have enough money to pay for it, the Oracle will take all your money and give a special oracularity which refers to Oracle machines. You won't get any experience for this and will "use up" your one chance at getting experience at the major level. Even the minor consultation will only give you 2 points afterwards. This can be trouble if you were relying on this for a pacifist character.

Lists of consultations

The oracle's consultations are stored in plain text in the source code, you can read the:

Mythology and history

The Oracle is primarily based on the Pythia, the priestess who presided over the Oracle of Apollo at Delphi; the NetHack Oracle will welcome you to "Delphi" when she spots you arriving at her abode. Some behavior is also in reference to the Internet Oracle from rec.humor.oracle, which first appeared in 1989, as did the Oracle in NetHack 3.0.0.

Both of these predate the Oracle in The Matrix film series, which is not referenced.

The Oracle-level sound effects reference several different oracles:

You hear a strange wind.

The Oracle of Jupiter at Dodona

You hear convulsive ravings.

The Oracle of Apollo at Delphi

You hear snoring snakes.

The Oracle of Æsculapius at Epidaurus

The two hallucination sounds both reference the Internet Oracle:

You hear someone say "No more woodchucks!"

In reference to the taboo question "How much wood would a woodchuck chuck if a woodchuck could chuck wood?"

You hear a loud ZOT!

In reference to the traditional answer to this.

Strategy

The Oracle will not get angry if you dry up the fountains or destroy the statues.

If you lack telepathy, the Oracle level can often be recognized by its slightly different assortment of monsters, e.g. naga hatchlings and baby dragons. This is because it counts as neutral for monster generation purposes, just like Sokoban.

UnNetHack

UnNetHack also makes a few minor adjustments to the Oracle level. The level is generated with 1 guaranteed woodchuck.
In addition, monster generation is slightly different on the Oracle level.
93% of monsters generated will be by the normal mechanism.
The remaining 7% of monsters generated will be according to the following probabilities:

Encyclopedia entry

Delphi under towering Parnassus, where Apollo's oracle was,
plays an important part in mythology. Castalia was its
sacred spring; Cephissus its river. It was held to be the
center of the world, so many pilgrims came to it, from
foreign countries as well as Greece. No other shrine rivaled
it. The answers to the questions asked by the anxious
seekers for Truth were delivered by a priestess who went into
a trance before she spoke.